The seven numbers that follow the BP_APPEARANCE_MODIFIER:"category" represent the distribution of the given body part in the category indicated (in your case, round vs narrow eyes).
The seven numbers create the ranges which the game will randomly generate a value in for the creature's body part. Each number range of the seven set points (which actually equates to 6 ranges) has an equal chance of being selected and then populated by a number. At least I think so given how other appearance modifier tokens work.
So in essence, the first number of the seven is the minimum, the last number is the maximum, and the other 5 numbers create the blocks of the numbers in between for the game to chose from to populate.
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The description point for the given selected body part (like extremely narrow, very narrow, slightly narrow, ect. for round-vs-narrow) is dictated by another token,
[APP_MOD_DESC_RANGE:#:#:#:#:#:#]
If APP_MOD_DESC_RANGE isn't included under the SET_BP_GROUP: token, I think the game defaults to a set description range, or uses the BP_APPEARANCE_MODIFIER range as the description range. I'm not sure which. If the game does just use the BP_APPEARANCE_MODIFER range, then you should have an equal probability of all description types unless you include the APP_MOD_DESC_RANGE token.
If you use APP_MOD_DESC_RANGE, then the numbers that follow determine the number ranges where the appearance modifier is used. So if your range is 30:60:90:110:150:190, then the ranges of description are 'minimum'-30, 31-60, 61-90, 91-110, 111-150, 151-190, and 191-maxium (whatever your minimum and maximum are from the BP_APPEARANCE_MODIFIER ranges).
These regions equate to lowest:lower:low:median:high:higher:highest description for that body part category.
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So if you wanted to create a creature whose eyes are, on average, very narrow, you might want a range like
[BP_APPEARANCE_MODIFIER:ROUND_VS_NARROW:0:5:10:15:20:25:30]
[APP_MOD_DESC_RANGE:15:30:40:50:60:70]
[APP_MOD_NOUN:eyes:PLURAL]
This should result in a creature with equal chances of extremely narrow and very narrow eyes, and never with any eye description other than those, because your modifier range only permits values between 0 and 30, which are the values for the first two description ranges in APP_MOD_DESC_RANGE. The numbers after 30 (the 40:50:60:70) don't really matter in this case and could in theory be just about any number, because your BP_APPEARANCE_MODIFER string won't create anything beyond 30.
Make sense?